Band carrier selector system



Get. 25, 1938. F K, ViQEELAND 2,134,677

BAND CARRIER SELECTOR SYSTEM Filed Aug. 14, 1935 4 SheetsSheet 1 OUTPUT INVENTOR FREoEmcK K. \/REELAND ATTORNES Oct. 25, 1938. K ND 2,134,677

BAND CARRIER SELECTOR SYSTEM Filed Aug. 14, 1935 4 Sheets-Sheet 2 5 50.

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INVENTOR FREDERMK KVREELAND ATTORNEYZ Oct. 25, 1938. F, K VREELAND 2,134,677

BAND CARRIER SELECTOR SYSTEM Filed Aug. 14, 1935 4 SheetsSheet 3 FREDE RICK K Vazn/m 0 BY 6 g 5 RNEYS Oct. 25, 1938.

F. K. VREELAND. 2,134,677

BAND CARRIER SELECTOR SYSTEM Filed Aug. 14, 1935 4 Sheets-Sheet 4 ammmn INVENTOR azucm x K Vnzzm w ATTORNE :6

Patented Oct. 25, 1938 UNITED STATES PATENT oFFicE 12 Claims.

The invention herein set forth is an improvement in receivers for modulated signal waves. It is particularly applicable to receivers of the type that I have heretofore designated as band selectorsystems, which are characterized by the fact that the various frequencies in the transmission band of the modulated wave are received with substantial uniformity with a sharp cut-off at the extremities of the band giving full fidelity of reception combined with high selectivity. The present improvement is directed to increasing still further the selectivity and sensitivity of the system without sacrificing its fidelity or other desirable properties. i

These results are accomplished by utilizing the variable phase relation that exists between the currents in the several elements of a band selective unit of the type employed combined with the principle of regeneration in such a way that super-amplification is appliedto one of the frequencies to which the band selector unit is responsive while the other frequencies of the reception band are received in:their true relative proportions. By adjusting the system so that the frequency which is super-amplified coincides withthe carrier frequency of the modulated signal wave to be received, the ratio of the carrier amplitude to the amplitudes of the side band frequencies, as received, is increased while the relations of the side band amplitudes to each other are not altered. By this means a large increase in selectivity and sensitivity is securedwithout any sacrifice of fidelity and the construction of theapparatus is greatly simplified by the elimination of amplifiers and selective circuits which are rendered unnecessary. Also great simplicity in operating and adjusting the apparatus is secured.

By the use of certain specific arrangements of the invention hereinafter described the superamplified frequency may be made the midfrequency of the reception band of the band selective unit in which case both side bands of the transmitted wave are received in their true relations, or it may befmade one or the other of the limiting frequencies of the reception band, in which case only one of the side bands will bereceived. By the use of the latter arrangement full fidelity of reception is secured by the use of only half the band width that is ordinarily required, thus securing an added element of selectivity and a simplification in the'design of the circuits and increasing the number of broadcast channels which may be, included in a given frequencyband. l y 1 -'I'hese desirable features are securedby combining the band selective unit with means for producing regeneration in such unitin the manner herein set forth.

Theform of band selective unit that is preferably employed is described in my U. S. Patent 1,725,433. It comprises two reactive couples; each having reactances that are partly balanced at the frequencies included in the transmission band, combined with a reactance common to both couples whose value is so related to the reactances of the couples that the unbalanced portion of these reactances is balanced and the system is made responsive to all frequencies within the transmission band. A characteristic feature of this system is the fact that the phase relation between the currents in the two reactive couples varies with the frequency from approximate synchronism, at one limiting frequency of the band, to approximate opposition at the other limiting frequency. This feature makes it possible to select one of the frequencies of the band, such as mid-frequency, or one of the limiting side frequencies, and by the use of suitable connections produce regeneration at this frequency, giving super-amplification, as will be explained.

The principles of regeneration, which are now well understood, were set forth in my U. S. Patents Nos. 829,447 and 829,934 of 1906; namely, utilizing the oscillations of an oscillating circuit to produce a field which controls the flow of current in a sensitive gap, producing commutation of the energy from an external source and feeding the commutated energy into the circuit in synchronism with the oscillations. One of the means described for effecting the commutation was employing an electrostatic field to control the dischargeof cathode particles in a vacuum tube.

The use of regeneration in a three electrode thermionic tube, as the sensitive gap, to intensify an incoming signal without producing oscillations was shown in Armstrongs U. S. Patent No. 1,113,149.

In carrying out the present invention the principle of regeneration is employed to select a single frequency out of a band of frequencies to which a circuit is responsive, by virtue of its phase relation, which distinguishes it from other frequencies to which the circuit is also responsive, and super-amplify the incoming oscillations of this particular frequency so that they are received with an amplitude that is greater, and preferably much greater than the relative amplitude of the other frequencies in the band to which the circuit is responsive. Preferably the frequency that is selected for super-amplification is the carrier frequency of the incoming modulated signal wave. The other or side band frequencies are received in their true relative proportions, without distortion, because of the band selective property of the circuit.

The regeneration by which the selective superamplification is produced is obtained preferably by the use of one or more thermionic amplifier tubes of the well known types with circuit connections associating 'these tubes with the band selective circuit or circuits in such manner that the potentials that are impressed on the control electrode by the oscillations of the selected frequency in the band selective circuit have the proper phase relation when amplified by the amplifier tube or tubes to reinforce the oscillations of the same frequency in the band selective circuit.

The particular frequency in the response band of A the band selective circuit that is selected for reinforcement and, super-amplification depends on the phase relations of the particularcircuit and on the feed-back connections employed for the reenforcement. For example if in a given arrangement the feed-back connections do not produce any phase shift, one of the limiting frequencies of the band may be reinforced or super-amplified. If the feed-back connections are arranged to produce a full reversal of phase, the other limiting frequency may be reenforced since currents of this frequency in the band selective unit have substantially the opposite phase relation to those of the first named limiting frequency. If two similar bandselective units are employed in cascade, the frequency that is super-amplified may be that at which each unit produces a phase shift of quadrature, namely a mid-frequency. Thus the frequency that is selected out of the reception band for super-amplification is selected automatically in accordance with the particular feed-back connections employed by virtue of the dependence of the phase relation of the several currents and the corresponding potentials in the band selective unit on their frequency; This dependence of the phase relation on the frequency is fully explained in my Patent No. 1,725,433, and illustrated in Fig. 2 thereof.

7 When the band selective unit or units are constructed or adjusted so that the frequency selected for super-amplification is the carrier frequency of the received modulated wave, a great increase in sensitivity is produced, since the effective strength of the signal received depends upon the received amplitude of the carrier frequency. When the demodulator employed is of the square-law type, which is usually preferable, the effective. signal strength is proportional to the received carrier amplitude. Thus if the carrier is super-amplified in relation to the side band frequencies to ten times its relative amplitude in the incoming transmission band. for example, -the increase in sensitivity will be ten fold. The selectivity, is correspondingly increased because of the sensitive adjustment to the carrier frequency due to 'the regeneration and because interfering signals are not only excluded by the, cut off of 'theband selector but also they are not super-amplified as the desired signals are sincetheir carrier is not. Thus the selectivity is increased in the case cited for example ten fold.

The increased selectivity and sensitivity are secured without'anysacrifice of fidelity since all the tones corresponding to the several side band frequencies are received in their true proportions, all being multiplied in the same ratio by the super-amplification of the carrier. The fidelity is in fact increased since the false overtones that are ordinarily produced by interaction of the side band frequencies with each other, or by detector distortion, are not subject to the super-amplification that the true tones have, so their relative intensity is reduced to a negligible amount. This advantage of the invention is particularly apparent when full modulation is I employed in the transmitter.

' Various embodiments of the invention are i1- lustrated in the accompanying drawings.

In the drawings, Figures 1, 2, 3 and 4 show typical arrangements embodying the invention in a single amplifier stage.

Figures 10, 1a., 2a, 3a, 30, 4a and 4c are graphs showing characteristic curves of the apparatus in its several arrangements.

Figures 1b, 2b, 3b, 4band 4d show the relations of such characteristic curves to the transmission band of a modulated wave which the apparatus is adapted to receive.

Figure 5 shows an embodiment of the invention including two amplifier stages.

Figure 5a is a typical characteristic curve of the last named arrangement and Figure 5b shows the relation of such curve to the transmission band of a modulated wave that it is adapted toreceive.

Figure 6- shows an application of the invention to a radio receiving apparatus of condensed and simplified form.

Figure 7 shows an arrangement in which the regeneration is automatically controlled.

Figure 1 is a schematic diagram illustrating the essential elements of the invention, minor details such as power supply, etc. being omitted for clearness. In the figure T1 and T2 are amplifier tubes, preferably of the well known thermionic type, the output of the first tube T1 being coupled to the input of the second tube T2 by a band selective coupling unit S. The form of band selective unit here shown is one of the forms set forth in my U. S. Patent 1,725,433 and illustrated for example in Figure 6. The particular form of circuit here illustrated is the species employing an inductance X3 as the common or band forming reactance of the band selective unit. The form of feed-back arrangement here shown is a connection F between the grid G2 of the second amplifier tube T2 and the grid G1 of the first amplifier tube T1. This feedback connection includes means for controlling the magnitude of the feed-back and thus regulating the amount of regeneration. The particular means here shown is an adjustable condenser E of suitable small capacity. It will be understood, however, that any of the well known equivalent means of producing and controlling a regenerative feed-back may be employed.

The operation of the apparatus is as follows:

When a modulated signal wave is impressed on the input terminals marked Input with the feed-back circuit F open or inoperative, the various component frequencies of the input wave are transmitted through the band selective unit, which is arranged to pass a band of frequencies including the input wave, and are delivered with amplified energy to the output terminals marked Output. A typical response curve of such an apparatus is illustrated in Figure 10, F1 and F2 being the limiting frequencies of the band, as

fully explained in my aforesaid patent. The characteristic curve Figure 1c is equivalent to the curve Figure 3 of said patent, the vertical scale being compressed and the horizontal scale expanded for convenience in illustrating the present invention. As explained in the patent the phase relation between the potentials at points 0 and d of the band selective unit varies with the transmitted frequency through approximately 180, the potentials at these points being substantially in synchronism at one limiting frequency of the band F2, and approximately in opposition at another limiting frequency of the band F1, the phase relation having intermediate values at intermediate frequencies.

If the direction of windings and connections of the apparatus is such that the potential at the point 0 has a phase relation suitable for producing regeneration when connected to the grid G1 of the amplifier tube T1, then when the feedback connection F is employed, the potential at point d should have the same phase relation as the point c. This condition is fulfilled in the arrangement shown at or near the limiting frequency F2. As a result of this connection superamplification is produced by regeneration at this frequency. When the degree of regeneration is suitably controlled as by adjusting the small condenser E the super-amplification increases the output amplitude at this frequency to many times the substantially constant output amplitude at other frequencies within the reception band of the band selective unit. The resulting characteristic curve of the apparatus is illustrated in Figure 1a; the response curve being substantially flat at frequencies between F1 and F2, with an abrupt high peak at the frequency of super-amplification F2.

In operating the apparatus for the reception of a modulated signal wave it is arranged or adjusted, as for example by varying the condensers C1 and C2, so that the frequency of super-amplification F2 coincides with the carrier frequency of the modulated signal wave. The incoming oscillations of carrier frequency will then be super-amplified to a degree much greater than the amplification of the side band frequencies which are amplified insubstantially constant degree between the limiting frequencies F1 and F2 of the reception band. Frequencies lower than F2 will however not be amplified since they lie outside of the reception band of the band selective unit.

This relation of the reception band to the transmission band is illustrated by comparison of Figure 1a and Figure 1b. In Fig. 117, C represents the carrier frequency, C B1 being the upper side band and C B2 being the lower side band. When the frequency of super-amplification F2, Figure la, is made tocoincide with the carrier frequency C Figure 1b, it will be seen that the upper side band C B1 lies within the reception band F2 and F1 and is received, while the lower side band C B2 lies outside of the reception band and is not received. a i

This feature of receiving only one of the two transmitted side bands is of great practical value since it reduces-the width of the channel required for transmitting the modulated signal one-half without loss of fidelity.

It will be understood that the super-amplification of the carrier frequency greatly increases the sensitivity of the apparatus since the amplitude of any received audio frequencydepends both on the amplitude of the corresponding side band frequency and on the amplitude of the received carrier frequency; When the amplitude of the received carrier frequency is increased by super-amplification the received amplitude of all the audio frequencies due to modulation is correspondingly increased. If the demodulator employed is of the square-law type, which is preferred, the increase in sensitivity will be proportional to the degree of super-amplification of the carrier. In Figure 1 the amplifier tube T2 is shown with agrid condenser and leak D arranged for demodulation.

It will be understood that all audio frequencies while thus emplified are nevertheless received in their true relative proportions since the super-amplification applies alike to all frequencies within the fiat reception band of the band selective unit. The highest fidelity is thus secured.

This invention also produces an increase in selectivity proportional to the degree of superamplification of the carrier, since all the .received frequencies belonging to the super-amplified carrier are intensified alike while foreign frequencies comprised in any other signal wave are not intensified, since their carrier frequency is not super-amplified. The selectivity inherent in the band selective unit is thus greatly augmented and the apparatus becomes selective to a degree far greater than that attained by any of the well known tuning systems which do not include this invention.

Various modified arrangements are possible. One such modification is shown in Figure 2. Here the apparatus is the same as that of Figure 1 except that the phase of the feed-back through the connection F is reversed. This may be accomplished in the manner shown through a transformer FR. having mutually reversed windings or connections. The adjusting condenser E may or may not be employed as may be expedient.

Because of the phase reversal of the feed-back connection, regeneration will now occur when the potential at point d is in opposite phase to the potential at point c. This condition is fulfilled at the other limiting frequency F1 of the band selective unit. The result of this arrangement is super-amplification of the upper limiting frequency of the band F1 instead of the lower limiting frequency F2 as in the arrangement of Figure 1. The resulting characteristic curve is shown in Figure 2a.

The relation of this characteristic curve to the transmission band of the modulated signal Wave, Figure 2b, is also illustrated. When the apparatus is arranged or adjusted so that the superamplified frequency F1 coincides with the carrier frequency C of the modulated wave, then the lower sideband C B2 is received, and the upper side band C B1 is not received. The result when demodulated is the same as that in the arrangement of Figure 1 since both side bands have like effects when the received wave is demodulated.

. Figure 3 shows a modified arrangement in which the common or band forming reactance X3 amplified frequency again is the limiting frequency F2 which is now the upper limiting frequency, as shown in the characteristic curve Figure 3a. When the apparatus is arranged .or adjusted so that the frequency F2 coincides with the carrier frequency C of the transmitted wave as illustrated in Figure 3b, the lower transmission band will be received instead of the upper transmission band as in Figure 1.. In this respect the result is similar to that achieved by the arrangement of Figure 2... j

The arrangement of Figure 4 differs from the above described arrangements in using the third species of the band selective unit described in Patent No. 1,725,433 namely that in which the common or band forming reactance is a mutual inductance. This mutual inductance is indicated in the figure by the mutual inductive coupling X2 between the inductances L1 and L2 of the two reactive couples of the band selective unit.

When this arrangement is employed the superamplified frequency will be either the lower limiting frequency of the reception band, as illustrated in Figure 4a, or the upper limiting frequency as illustrated in Figure 40 depending upon the direction of windings of the coils L1 and L2 and the sense of their mutual inductive coupling, as well as on the sense of the feed-back.

In the former case when the apparatus is arranged to make the super-amplified frequency coincide with the transmitted carrier frequency, the upper side band will be received as illustrated in Figure 4b. In the latter case the lower side band will be received as illustrated in Figure 4d.

Figure 5 illustrates an arrangement in which both side bands are received. In this arrangement two band selective units S1 and S1 are employed of the type illustrated in Figure 1. They are preferably coupled by an amplifier tube T2. To offset the reversal of phase occurring in the amplifier tube T2, there should be a corresponding reversal of phase in the two selective units S1 and S2, the connections being otherwise suitable for regeneration. If these two selective units are similar, then this phase reversal should be divided between them, that is, each band selective unit should produce a quadrature or 90 degrees phase shift. This condition is fulfilled in the arrangement shown, at the mid-frequency of the reception band of the two band selective units. This is shown as F in Figure So. When the regenerative feed-back is arranged in the appropriate sense, super-amplification will occur at this midfrequency as shown. When the apparatus is adjusted to make the super-amplified mid-frequency coincide with the carrier frequency C, Figure b, then both side bands of the transmitted wave will be received. In this case the band selective units should be designed to have a band of response twice as wide as that employed when only one side band is received as in Figures 1, 2, 3 and 4.

It will be understood that the invention is not limited to the particular types of band selective units illustrated, nor to the particular arrangements for regenerative feed-back that are illustrated. Nor is the invention limited to the use of only one or two band selective units or one or two amplifier stages. A great variety of arrangements may be employed provided the band selective unit is one in which the phase relation at the point from which the regenerative feed-back is derived varies with the frequency within the limits of the band of response and provided that the feed-back arrangement is connected in the proper sense tobring the feed back potential in the proper phase relation for producing regeneration at one of the frequencies included in the reception band. In general when the phase relation of the band selective unit or units varies with frequency at least from zero to 180 degrees approximately, it will always be possible to select a regenerative connection of the proper sense to produce regeneration at at least one of the frequencies included within the reception band. When more than two band selective units are employed the super-amplified frequency may be at some intermediate point in the reception band.

The various arrangements shown are adapted to receive modulated signal waves transmitted by radio or over wires, either in the form in which they are transmitted or after being stepped down to lower frequencies by heating with a local oscillation, as explained in my U. S. Patent No. 1,239,852.

Figure 6 shows a simple application of the invention to the reception of modulated radio signals. Here the band selective unit S is provided with a collector A for receiving the modulated radio waves and feeds into a multi-electrode tube T, where it is amplified and demodulated. The demodulated audio frequency output is returned through a transformer Tr. to a second pair of electrodes of the. tube T and there again amplified. A feed-back connection F, is provided from the radio frequency anode of the tube to a point of the input of the band selective unit. Super-amplification is then produced at a frequency which is made to coincide with the carrier frequency of the desired signal wave by adjusting the condensers C1 and C2 in the usual way. By such an application of the invention high selectivity, high sensitivity and full fidelity of reception are secured in an extremely simple and inexpensive apparatus employing no more than half the number of tubes and tuned circuits that would ordinarily be required to obtain similar results.

It is convenient to employ an arrangement in which the degree of regeneration and. superamplification is regulated automatically with or without manual means for further controlling the super-amplification. Such regulation of the regeneration may be accomplished by the use of an automatic governor of the type set forth in my U. S. Patent No. 1,926,129, or by other equivalent means. One such arrangement is shown in Figure 7. Here arectifier R is employed to rectify a current derived from the output of the amplifier. This rectification sets up a charge in the condenser C and the electro-motive force of this charge is applied to the control electrode G1 of the amplifier tube T1 through the input circuit as shown. When the output due to regeneration tends to become excessive, the control electromotive force due to the rectification of the output increases, diminishing the gain of the amplifier tube and so checking a further increase of the super-amplification. The point at which the super-amplification is thus limited may be controlled by a manual device such as the potentiometer E0.

Another arrangement for controlling the regeneration, which may be employed with or without the arrangement just described, comprises a resistance R1 inserted in the cathode connection of the tube T1 and traversed by the anode current. When regeneration becomes excessive and tends toward the oscillation point the increase in the anode current increases the drop in the resistance R1, applying a negative bias to the grid G1 and reducing the gain of the tube. The tube T1 is preferably one of a type in which the gain decreases rapidly with increasing bias.

It will be understood, however, that any other suitable means of controlling the regeneration may be employed.

What I claim is: V i

1. In a receiver of modulated signal waves, a band selective unit responsive to a band of frequencies of said waves in which the phase relations vary with the frequency, amplifying means operatively connected to said band selective unit, a regenerative feed-back for the ampliflying means derived from a point in said unit whose phase relation at one of the frequencies within the band of responseis suitable for causing regeneration at said frequency, connections whereby the feed-back cooperates with the amplifying means to select the said frequency automatically and produce superamplification at said frequency that is large compared with the response at other frequencies within the band of response, and means for causing the selected frequency of regeneration to coincide with the carrier frequency of the modulated sighalwave,

2. In a receiver of modulated signal waves, a band selective unit responsive to a band of frequencies of said waves in which the phase relations vary with the frequency, amplifying means operatively connected to said ban-d selective unit, a regenerative feed-back for the amplifying means derived from a point in said unit whose phase relationat one of the frequencies within the band of response is suitable for causing regeneration at said frequency, connections whereby the feedback cooperates with the amplifying means to select such frequency automatically and produce super-amplification at said frequency, connections whereby the band selective unit cooperates with the amplifying means to amplify the other frequencies within the band of response with substantial uniformity, means for causing the selected frequency of regeneration to coincide with the carrier frequency of the modulated signal wave, and demodulating means and connections whereby the super-amplified carrier and the modulation frequencies are simultaneously impressed thereon.

3. In a receiver of modulated signal waves, a band selective unit responsive to the carrier frequency and one of the side bands of said waves in which the phase relations vary with the frequency, amplifying means operatively connected to such band selective unit, a regenerative feedback for the amplifying means derived from a point in said unit whose phase relation at one of the limiting frequencies of the band of response is suitable for causing regeneration at said frequency, connections whereby the feedback cooperates with the amplifying means to produce super-amplification at said limiting frequency, connections whereby the band selective unit cooperates with the amplifying means to amplify the other frequencies within the band of response in lesser degree, and means for causing the frequency of regeneration to coincide with the carrier frequency of the modulated signal wave.

4. In areceiver of modulated signal Waves, a band selective unit responsive to a band of frequencies of said waves in which the phase relations vary with the frequency, an amplifier tube operatively connected to said band selective unit, a regenerative feed-back for the amplifier tube derived from a point in said unit whose phase relationat one of the frequencies within the band of response is suitable for causing regeneration at said frequency, connections whereby the feedback cooperates with the amplifying means to select such frequency automatically and produce super-amplification at said frequency that is large compared with the response at other frequencies within the band of response, means for causing the selected frequency of regeneration to coincide with the carrier frequency of the modulated signal wave, and means for automatically controlling the amount of regeneration and super-amplification.

5. In a receiver of modulated signal waves, a bandselective system comprising a pair of band selective units responsive to a band of frequencies of said Waves in which the phase relations vary with the frequency, amplifying means operatively connected to said bandselective system, a regenerative feed-back forthe amplifying means derived from a point in said system whose phase relation at a mid-frequency of the band of response is suitable for causing regeneration at that frequency, connections whereby the feedback cooperates with the amplifying means to select such mid-frequency automatically and produce super-amplification at such frequency, and means for causing said mid-frequency to coincide with the carrier frequency of the modulated signal wave.

6. The method of receiving a modulated signal wave which consists in receiving a band of frequencies comprised in such wave in their substantially true relative amplitudes and in phase relations that vary with the frequency, preferentially selecting one of these frequencies by virtue of its phase relation, super-amplifying the preferentially selected frequency with respect to the other frequencies of the received band and preserving with substantial fidelity the relative amplitudes of such other frequencies.

7. The method of receiving a modulatedsignal wave which consists in receiving a band of frequencies comprised in such Wave in their substantially true relative amplitudes and in phase relations that vary with the frequency, preferentially selecting one of these frequencies by virtue of its phase relation, super-amplifying the preferentially selected frequency with respect to the other frequencies of the received band, preserving with substantial fidelity the relative amplitudes of such other frequencies, causing the super-amplified frequency to coincide with the carrier frequency of the modulated signal wave and demodulating the band including the superamplified carrier frequency and such other fre-- quencies.

8. The method of receiving a modulated signal wave which consists in receiving a band of frequencies comprised in such wave in their substantially true relative amplitudes and in phase relations that vary with the frequency, preferentially selecting one of these frequencies whose phase relation is suitable for producing regeneration, super-amplifying by regeneration the preferentially selected frequency with respect to the other frequencies of the received band, and preserving with substantial fidelity the relative amplitudes of such other frequencies.

w 9. The method of receiving a modulated signal wave which consists in selectively receiving a band of frequencies comprising the carrier frequency and one side band of such wave in phase relations that vary with the frequency, preferentially selecting one of these frequencies by virtue of its phase relation, super-amplifying the preferentially selected frequency to an amplitude that is high compared with the relative amplitude of the other frequencies of the selectively received b and, causing the super-amplified frequency to coincide with the carrier frequency of the modulated signal wave whereby the carrier is super-amplified, preserving the true relative amplitudes of the modulation frequencies of the selectively received side band and demodulating the band including the super-amplified carrier frequency and the modulation frequencies.

10. The method of receiving a modulated signal wave which consists in receiving with substantial uniformity a band of frequencies comprised in such wave in phase relations that vary with the frequency, preferentially selecting one of these frequencies by virtue of its phase relation, super-amplifying the preferentially selected frequency to an amplitude thatis high compared with the relative amplitude of the other frequencies of the received band, causing the super-amplified frequency to coincide with the carrier frequency of the modulated signal wave whereby the carrier is super-amplified, preserving the true. relative amplitudes of the modulation frequencies, demodulating the band including the super-amplified carrier frequency and the modulation frequencies, and automatically controlling the degree of super-amplification.

11. The method of receiving a modulated signal wave which consists in receiving a band of frequencies comprised in such wave, including the carrier frequency and one side band and excluding the other side band of such wave, in phase relations that vary with the frequency, preferentially selecting the carrier frequency by virtue of its phase relation, and super-amplifying the selected carrier frequency with respect to the received side band frequencies 12. The method of receiving a modulated signal wave which consists in selectively receiving with substantial uniformity a band of frequencies comprised in such wave in phase relations that vary with the frequency, preferentially and automatically selecting one of these frequencies by virtue of its phase relation, super-amplifying the preferentially selected frequency to an amplitude that is high compared with the relative amplitude of the other frequencies of the received band, and preserving the true relative amplitudes of the other frequencies.

FREDERICK K. VREELAND. 

